There are several surgical and non-surgical modalities that require the precise delivery of medicines and drugs to the site of disease. Often, these sites may also require an implanted device or prosthesis in addition to deliver such drugs, to perform one or more sensory or stimulatory functions, such as in a heart electrophysiological assessment or neural scanning.
Inherently “conducting polymers” (π-conjugated conductive polymers) for example, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(pyrrole), polyanilines, polyacetylenes, polythiophenes, polymer blends thereof and non-conducting polymers with conducting dopants are useful as biocompatible polymeric coating materials for preexisting electrodes, probes and sensors, providing unique electrical, biochemical and electroactive properties. The inherently conducting monomers can comprise one or more of (3,4-ethylenedioxythiophene) (EDOT), pyrrole, anilines, acetylenes, thiophenes, and monomer blends thereof.
Several developments in the field of electrochemical delivery of bioactive agents have yielded electrode devices that incorporate a conducting polymer that is electrochemically cycled between a charged or neutral state. The premise behind this mode of operation includes employing a conducting polymer electrode wherein the conducting polymer is for example, charged cathodically or anodically while in contact with an aqueous medium. The drug to be delivered must exist in the form of a counterion causing the drug to bind ionically. Such devices are described in U.S. Pat. No. 4,585,652.
The use of such drug delivery is disadvantageous, since the selection of drug or pharmaceutical must comply with it's counterion function and limits the selection of bioactive substances to be delivered. Furthermore, the bioactive agent cannot comprise both anions and cations in a single delivery cycle and cannot deliver bioactives that do not have a specific charge or are neutral. Further limitations which are placed on the use of bioactive agents coupled to conducting polymers include limits on the amount of coupled bioactive agent to be delivered. Invariably, the upper limit of material that can be delivered in such delivery devices is around 50% of the polymer used, since there is a finite amount of charged conducting polymer to bind the chemical in its redox sites. (Typically one charge per three molecules of monomer).
It would be highly desirable to design electrode devices which could intimately interface electrode sites to living tissue, and thus create charge transport from ionically conducting tissue to the electronically conducting electrode and induce surrounding tissue to attach or interface directly to the implanted device and are capable of delivering any species of bioactive substance notwithstanding charge and quantity limitations.